A Review on Fire Behavior of Traditional and Dense Concretes

Fire behaviour of ordinary (traditional), dense and SCC concretes is reviewed. Concrete is usually known as a material with good fire resistance. However, the mechanical resistance of concrete reduces with rising temperature because of chemical and dimensional changes, which can result in failure of the concrete element. Concrete has considerable amounts of water, which with high thermal capacity and low thermal conductivity of concrete can result in a low heat transfer rate from hot surface to bulk of concrete and hence delay the failure of component in fire. In contradictory, these characteristics can result in producing high vapour pressure in regions near the surface and spalling of concrete, which reduces the fire resistance of element, especially when the cover of reinforcing bars fails. The risk is much higher in dense concretes, like HSC and HPC. During the expose of concrete to fire, simultaneous heat and mass transfer phenomana cause that humidity trnsfers into internal layers. The vapor pressure will be rised in a region near the surface and reached to a maximum in a distance, which depends upon heating rate, moisture content, porosity, properties of materials, environment conditions, etc. The spalling will be occurred, if tensile strength is less than this pressure. Dense concrets may suffer from spalling in conditions that is not a risk for normal concretes. Self-compacting concretes also show different behaviour from other concretes at high temperatures. This is due to different compounds and high content volume of powders. The powders may result in a consirable decrease in fire resistance of concrete, because of low thermal stability or rise of packing of system, which can cause spalling in early stages of fire.